Electrocoating compositions are well known and disclosed in Gilchrist patents, such as U.S. Pat. Nos. 3,351,675; 3,362,899; 3,575,909, and 3,351,575, and the same are incorporated herein by reference. Prior art electrocoating compositions are often cured by the inclusion of catalysts and followed by application of heat. More recently, electron beam polymerization of electrocoating compositions has been suggested in U.S. Pat. Nos. 3,501,390 and 3,501,391, and the same are incorporated herein by reference.
It now has been found that an unsaturated, water-dispersible ethylenically unsaturated polymer containing ultraviolet sensitizer can be solubilized in aqueous solutions and uniformly electrocoated onto the substrate while maintaining a critical ratio of sensitizer to polymer electrocoated onto the substrate. This invention provides an expedient and efficient solution to inherent problems pertaining to electrocoating a polymer susceptible to ultraviolet radiation curing. Such polymers must be rendered water soluble as well as curable by ultraviolet energy. Electrocoating compositions of this invention containing ultraviolet sensitizers are stabilized in the electrocoating bath to properly maintain a constant ratio of sensitizer to polymer. Up to about 5% photosensitizer is required to activate the polymer with actinic radiation and this ratio of polymer relative to a low percentage of ultraviolet sensitizer must be maintained when the composition is electrocoated onto the substrate so that a complete cure is achieved when exposed to ultraviolet light.
Accordingly, a primary object of this invention is to provide an electrodepositable composition containing a stabilized ratio of ultraviolet sensitizer dispersed in an ethylenically unsaturated polymer solubilized in aqueous solution that can be efficiently and uniformly electrocoated on a substrate and subsequently cured with ultraviolet energy.
A further object is to provide a process for solubilizing an ethylenically unsaturated polymer containing an ultraviolet sensitizer within an aqueous solution, electrocoating a constant ratio of ultraviolet sensitizer and polymer onto an anode conductive substrate to provide a paint film on the substrate, and irradiating the paint film with ultraviolet energy until the film becomes fully cured.
These and other advantages of the invention will become more apparent by referring to the Detailed Description of the Invention.